1. Field of the Invention
The present invention relates to an image forming apparatus including a fixing unit, and a fixing unit support method and a fixing unit position adjustment method for the image forming apparatus.
2. Description of the Related Art
In an electrophotographic image forming apparatus, an image is formed on a recording medium such as a sheet of paper or an OHP (overhead projector) film by charging a drum-like or belt-like rotating photosensitive element; irradiating the photosensitive element with light to form a latent electrostatic image thereon; attaching toner to the latent electrostatic image with a development device to make the latent electrostatic image visible as a toner image; transferring the toner image to the recording medium directly or indirectly via a belt-like intermediate transfer unit; and fixing the toner image on the recording medium.
Such an image forming apparatus includes a frame for reinforcing a body of the image forming apparatus against distortion or twisting. The frame is generally made of steel plate and includes a base member, a pair of opposing side plates set up on the base member, and stays or brackets laid between the side plates. In the frame, detachably attachable components such as a photosensitive device, a charging device, an optical writing device, a development device, a transfer device, a fixing device, an intermediate transfer device, and a recording medium feed device are usually provided in the form of a modular unit or a process cartridge including such units.
The fixing device, which is typically unitized for ease of maintenance, generally fixes an image on a recording medium when the recording medium passes through a fixing nip formed by a fixing member and a pressure member. The fixing nip is set parallel to the transfer rollers, etc., in recording medium feeders and transferring devices that transfer a recording medium to each transfer point and fixing point. When and if the fixing nip is angled with the transfer roller, etc., the transfer directions of a recording medium at the fixing nip and the transfer roller, etc., do not match, resulting in skewing of the recording medium and production of abnormal images transformed in a trapezoidal manner, etc.
As a method of preventing such skewing, pursuing component parts tolerances to perfection is practically difficult in light of cost increase as well as from a technical point of view. Furthermore, since there are a number of parts in an image forming apparatus, the tolerances of individual parts such as a fixing unit and a recording medium feeder are cumulative and directly affect the relative positions of these devices, easily displacing them from their parallel positions. In addition, there are part or unit assembly errors to be considered which are difficult to eliminate completely.
In addition, an assembly jig is required for assembling an image forming apparatus, and naturally, highly accurate design and manufacturing are demanded therefor. However, even with such a highly accurate jig, there is a limit to improvement in the accuracy with which devices are positioned parallel to each other.
Although the situation is as described above, to meet current demand for high definition quality images it is desired that an image forming apparatus has recording medium transfer devices, including a fixing unit; that are positioned parallel to each other with a high degree of precision.